Defaults.Exposed › September 2026 census › v10 registry › MIME-sniffing protection
MIME-sniffing protection
Methodology v10 · canonical ID x-content-type-options · Web Security · scored · census as of September 5, 2026
Stops browsers mis-reading files in ways attackers can abuse.
Definition
| Canonical ID | x-content-type-options |
|---|---|
| Category | Web Security |
| Grade impact | Scored, counts toward the grade |
| Pass | The site sends X-Content-Type-Options: nosniff. |
| Fail | The header is absent. |
| Example (passing) | X-Content-Type-Options: nosniff |
No-data rule: when this check couldn't be determined for a domain (timeout, SERVFAIL, redacted source) it returns N/A and is excluded from that domain's scoring denominator: "couldn't determine" is never counted as a failure. "Determined absent" is a real fail.
Prevalence across the census
17.8% of domains whose page returned a 2xx response send X-Content-Type-Options: nosniff (22,381,337 of 125,815,036, as of September 5, 2026).
Census denominator: 316,600,902 graded domains; this check is measured only against domains whose page returned a 2xx response (125,815,036). Aggregates only: never an individual domain's result.
Fix it
Plain-English impact, cost of ignoring it, and step-by-step remediation: defaults.exposed/fix/mime-sniffing
Cite this check
Defaults.Exposed, "MIME-sniffing protection (x-content-type-options)", Grading Methodology v10 (census as of September 5, 2026). https://defaults.exposed/methodology/x-content-type-options
Permalink: https://defaults.exposed/methodology/x-content-type-options ·
All 34 checks: v10 registry ·
Machine-readable: /methodology/checks.json ·
Licence: open data